1. Field of the Invention
The present invention relates to a pyrometer and method for measuring the temperature of turbine blades accurately by eliminating or substanitally reducing the effect of reflected radiation from frame or hot carbon particles.
2. Description of the Prior Art
Pyrometers are well known in the art. Also, the use of various optics for receiving radiation being emitted from bodies has been known. U.S. Pat. No. 4,222,663 issued to Gebhard et al. on Sept. 16, 1980, is for an optical pyrometer and technique for temperature measurement, which utilizes an apparatus for correcting errors due to reflected energy from the device being analyzed. A pair of detectors see the same target, but at least one detector has its input filtered, so that the wave length interval of one detector is contained within the other. Conventional detectors are utilized for generating output voltages that are analyzed in a high speed computer. The computer produces an output that compensates for the presence of reflected energy by estimating the magnitude of the reflected energy componet through the calculations. The patent contains no teaching of simplifying the elimination of the reflected radiation component from a turbine blade, as is done in the present application.
U.S. Pat. No. 4,222,663 shows that detectors are conventional, and filters are conventional and also mentions that fiber optic bundles can be utilized.
A two color pyrometer is shown in U.S. Pat. No. 3,715,922 which utilizes two photo devices responding to different wavelengths and teaching the ability to provide a measure of the ratio of received radiation intensities at the two different wavelengths.
Another two color pyrometer is shown in U.S. Pat. No. 3,992,943 used for monitoring the radiation densities of two different wavelengths, which are used for obtaining an indication of temperature. Again, however, there is no teaching of providing weighting factors to output signals from the detectors for eliminating the effect of reflected flame radiation in a turbine.
United Kingdom Pat. No. 2,045,425B shows improvements in pyrometers that provide a scheme for removing errors that are due to the presence of spurious sources of heat. The device also was used specifically for turbine blade temperature measurements, and the specification points out that the measurements can be degraded by the transitory presence of hot carbon particles from the combustion chamber. Thus, while British Pat. No. 2,045,425 points out the problem that is faced, the solution suggested therein requires more complex circuitry than the present device, and does not simplify the use of signal measurements as with the present device.
French Patent Publication No. 77-28335 (2,365,108) relates to an optical system for measuring the temperature of the fins of a turboreactor, and includes filters for passing radiation at two different wavelengths, and detectors that separately detect the radiation levels and provide output signals that are amplified and then passed to a divider circuit that in turn produces analog signals that are representative of the ratio of the amplitudes of the signals from the detectors. The analog signal from the output divider circuit is used in a central processing unit to provide the appropriate measurement of the temperature of the fins of the turbine. However, here too, the use of a weigthing factor in the output from one of the radiation detectors to provide a ratio constant to simplify the detection of actual temperature of the turbine blade is not shown.
U.S. Pat. No. 4,326,798 also shows a pyrometer system with a measurement of temperature from a source of heat which might be contaminated by radiation from a transient spurious source of heat at a higher temperature, and it provides filters to divide radiation detected directly from a turbine blade into two channels which are separately detected and wherein their outputs are divided and fed to a threshhold detector to provide a "flag" output signal if the ratio between the outputs of the two detectors exceeds a predetermined value to thereby indicate an erroneous temperature reading due to the presence of hot carbon particles. Additionally, FIG. 4 of this patent provides output amplifiers from each of the detectors, and provides a scaling factor circuit on the output of one of the amplifiers, which is then fed to a subtraction circuit. However, selecting the proper scaling factor for providing a direct indicator of actual blade temperature, by making the scaling factor proportional to the ratio of the portions of the detector outputs that are attributable to the presence of flame or hot carbon particles is not taught.